Podcast
Questions and Answers
What is the main purpose of the preamble in an Ethernet frame?
What is the main purpose of the preamble in an Ethernet frame?
What does a Frame Check Sequence (FCS) do?
What does a Frame Check Sequence (FCS) do?
Which value in the type field of an Ethernet frame indicates that the length of the encapsulated packets is specified?
Which value in the type field of an Ethernet frame indicates that the length of the encapsulated packets is specified?
What is the format of the MAC address used in Ethernet frames?
What is the format of the MAC address used in Ethernet frames?
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What is the total byte size of an Ethernet frame including its header and trailer?
What is the total byte size of an Ethernet frame including its header and trailer?
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What hex value indicates an encapsulated IPv4 packet in the type field?
What hex value indicates an encapsulated IPv4 packet in the type field?
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What does the Start Frame Delimiter (SFD) signify in an Ethernet frame?
What does the Start Frame Delimiter (SFD) signify in an Ethernet frame?
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What is the function of the destination address in an Ethernet frame?
What is the function of the destination address in an Ethernet frame?
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What type of message is used by a device to request the MAC address of another device?
What type of message is used by a device to request the MAC address of another device?
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What is the primary purpose of a MAC address?
What is the primary purpose of a MAC address?
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Which statement is true about the ARP Reply message?
Which statement is true about the ARP Reply message?
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What does the command 'arp -a' do?
What does the command 'arp -a' do?
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Which of the following formats represents a MAC address correctly for Cisco devices?
Which of the following formats represents a MAC address correctly for Cisco devices?
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What is the role of the Organizationally Unique Identifier (OUI) in a MAC address?
What is the role of the Organizationally Unique Identifier (OUI) in a MAC address?
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When using the ping command, which two messages are exchanged?
When using the ping command, which two messages are exchanged?
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What happens to dynamic MAC addresses in a MAC address table after 5 minutes of inactivity?
What happens to dynamic MAC addresses in a MAC address table after 5 minutes of inactivity?
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What is a characteristic of half duplex communication?
What is a characteristic of half duplex communication?
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What is the minimum payload size for an Ethernet frame if the header and trailer total 18 bytes?
What is the minimum payload size for an Ethernet frame if the header and trailer total 18 bytes?
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What state do router interfaces have by default due to the shutdown command?
What state do router interfaces have by default due to the shutdown command?
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Which entry type in the ARP table indicates an address learned dynamically?
Which entry type in the ARP table indicates an address learned dynamically?
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Which type of frame is specifically intended for communication with a single target device?
Which type of frame is specifically intended for communication with a single target device?
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What information is found in the MAC address table of a switch?
What information is found in the MAC address table of a switch?
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Which option describes MAC Address Tables in relation to ARP?
Which option describes MAC Address Tables in relation to ARP?
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What occurs when an Ethernet frame is considered an unknown unicast?
What occurs when an Ethernet frame is considered an unknown unicast?
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What is a characteristic of devices connected to a hub?
What is a characteristic of devices connected to a hub?
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What is the purpose of the jamming signal in CSMA/CD?
What is the purpose of the jamming signal in CSMA/CD?
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What happens during speed/duplex autonegotiation?
What happens during speed/duplex autonegotiation?
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What will occur if autonegotiation is disabled on a device connected to a switch?
What will occur if autonegotiation is disabled on a device connected to a switch?
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Which of the following defines a 'giant' frame?
Which of the following defines a 'giant' frame?
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Which type of error is characterized by frames that are smaller than the minimum size?
Which type of error is characterized by frames that are smaller than the minimum size?
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What is indicated by an output error on a switch?
What is indicated by an output error on a switch?
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Which Ethernet speed supports the highest capacity among the following options?
Which Ethernet speed supports the highest capacity among the following options?
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Study Notes
Ethernet Frame Structure
- Ethernet frames consist of a header, payload (packet), and trailer, with a total of 26 bytes (4 bytes for FCS, 7 bytes for preamble, 1 byte for SFD, 6 bytes for destination MAC, 6 bytes for source MAC, and 2 bytes for the type/length).
Preamble and Start Frame Delimiter (SFD)
- The preamble is 7 bytes of alternating 1s and 0s (10101010 * 7) enabling device synchronization.
- SFD is 1 byte (10101011), marking the end of the preamble and the start of the frame.
MAC Addresses
- MAC addresses are 6 bytes (48 bits) long and uniquely assigned to devices (also known as Burned-In Addresses).
- First 3 bytes are the Organizational Unique Identifier (OUI), assigned to manufacturers.
- Different formatting examples include:
- Windows: 5C-23-5A-24-2B-3D
- Cisco devices: 0011.5CCC.5C00
- Linux and IOS: 5C:23:5A:24:2B:3D
Type/Length Field
- This 2-byte field indicates either the length of the encapsulated packet (if ≤ 1500) or its type (if ≥ 1536) with IPv4 and IPv6 specified as 0x0800 and 0x86DD respectively.
Frame Check Sequence (FCS)
- The FCS field is 4 bytes long and employs a Cyclic Redundancy Check (CRC) algorithm to detect data corruption.
Ethernet Frame Minimum and Maximum Sizes
- Minimum Ethernet frame size (header + payload + trailer) is 64 bytes, requiring a minimum payload of 46 bytes.
- If the payload is less than 46 bytes, padding bytes are added.
Address Resolution Protocol (ARP)
- ARP facilitates discovering a device's MAC address based on its known IP address, utilizing two message types: ARP Request (broadcast) and ARP Reply (unicast).
- ARP tables can be viewed using
arp -a
in the command prompt, showing dynamic and static entries.
Ping Utility
- Ping tests network reachability between devices and measures round-trip time using ICMP Echo Request and Echo Reply messages.
Switch Interfaces and CLI Commands
- Switch interfaces are in an up/up state by default if connected, while router interfaces are down by default until activated.
- Common commands include
show ip int br
to check interface status.
Duplex Modes
- Half duplex allows either sending or receiving at one time, required by devices connected to hubs.
- Full duplex enables simultaneous sending and receiving, commonly utilized in switch configurations.
CSMA/CD Protocol
- Carrier Sense Multiple Access with Collision Detection (CSMA/CD) allows devices to listen for traffic before transmitting to prevent collisions.
- On collision, devices send a jamming signal and wait a random time before trying again.
Speed/Duplex Autonegotiation
- Switch interfaces default to auto settings for both speed and duplex; speeds include 10 (E), 100 (F), and 1000 (G) Mbps.
- If autonegotiation is disabled, the switch defaults to the slowest supported speed.
Interface Errors
- Common frame errors include:
- Runts: Frames smaller than 64 bytes.
- Giants: Frames larger than 1518 bytes.
- CRC: Failed frames based on FCS.
- Input and output errors indicating frame processing issues.
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Description
Test your knowledge on Ethernet LAN concepts as outlined in Module 5. This quiz covers topics such as switching, Ethernet frames, and the structure of data packets. Prepare to dive into the essential components that form the backbone of local area networks.